Final answer:
The heart is a triangular organ located in the mediastinum with two thirds of its mass to the left of the body midline and one third to the right. It is about the size of a fist.
Step-by-step explanation:
The triangular organ located in the mediastinum with two thirds of the mass to the left of the body midline and one third to the right is the heart.
The heart is a muscular organ that pumps blood throughout the body, supplying oxygen and nutrients to the tissues. It is about the size of a fist and is broad at the top, tapering towards the base.